We move on to the mystery outside seattle. The surprise thud from the sky in a normally quiet neighborhood there. Look at thuge piece of dented metal about the size of a refrigerator. It is actually the door to a jumbo jet. Abc's john schriffen working the phones with the faa today. So far they're unwilling to say where that door came from. Reporter: It seemed like a regular morning when suddenly this massive object, the size of a refrigerator door, came plummeting down from the sky. We heard a big crash like a slap, slap, and it did sound like a big, large piece of metal. Reporter: Turns out that mysterious object was a landing gear door from a 767 according to the faa. But where did the door come from? Just moments before it crashed friday, neighbors described what looked like a cargo jet flying unusually low. It sounded a little -- maybe it was -- distressed. Yeah, distressed or vibrating. What could have happened in this instance as the aircraft was coming in to land in seattle, the force of the air on the landing gear door could have torn off an already weakened gear door that may have then led to this piece of metal going into the residential area. Reporter: Back in may, cell phone-sized pieces of an air canada boeing 777 scattered onto cars near toronto. Just days before, the main cabin door from a small charter jet landed in the middle of a fairway on a miami golf course and in 2009, a dozen houses and numerous cars in brazil were reported damaged when parts, one fell from a cargo freighter. And back to this latest incident in washington state, it's believed there was a marking on the door meaning it was registered with the faa, but the agency tells me it could be weeks before we learn the plane the door actually came from. David, good news, no one

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